In a typical communications network, also referred to as e.g. a network, a system or a communication system, a centralized unit, located at a central location, e.g. a service provider central office, is connected to one or more remote nodes. More than one remote node may be connected to the same centralized unit by means of passive or in some cases, active, intermediate elements. The remote node(s) is located apart from the centralized unit and may be seen as an endpoint in a point-to-multipoint network. The centralized unit may be represented by e.g. an Optical Line Terminal (OLT) or an aggregation switch, where the term aggregation indicates that a plurality of remote nodes is connected to the aggregation switch.
An access network is that part of a communications network that connects a remote node(s) to its immediate service provider. It is contrasted with the core network. The core network is the central part of the communications network, which provides various services to the remote node(s) that are connected by the access network. In e.g. a Passive Optical Network (PON), downstream signals, i.e. from the centralized unit to the remote node(s), are broadcast to all remote nodes sharing a single communications channel. In other (non-PON) access networks, there may be a dedicated channel, e.g. fibre, microwave or copper Digital Subscriber Line (DSL), between each remote node and the centralized node. Upstream signals are signals transmitted from the remote node(s) to the centralized unit.
The remote node(s) may be a device by which a subscriber may access services offered by an operator's network and services outside the operator's network to which the operator's access network and core network provide access, e.g. access to the Internet.
The remote node(s) may be any device, enabled to communicate over a channel in the communications network, for instance but not limited to e.g. user equipment, sensors, meters, household appliances, medical appliances, media players, cameras, Machine to Machine (M2M) device, Optical Network Unit (ONU), Digital Subscriber Line Access Multiplexer (DSLAM), radio terminal or any type of consumer electronic, for instance but not limited to television, radio, lighting arrangements, tablet computer, laptop or Personal Computer (PC).
The remote node(s) is enabled to communicate with the network, wirelessly or wired.
When the remote nodes are wirelessly connected, the network may cover a geographical area which may be divided into cell areas, and is therefore called a cellular network. Each cell area is served by a Radio Base Station (RBS), which sometimes may be referred to as e.g. base station, evolved Node B (eNB), eNodeB, NodeB, B node, or Base Transceiver Station (BTS), depending on the technology and terminology used. The radio base station is designated RBS in some of the drawings.
An example of a communications network will now be described. The communications network may be a PON which is a point-to-multipoint network architecture that brings optical fiber cabling and signals all or most of the way to the end remote node(s). A PON comprises an OLT i.e. the centralized unit, at a service provider's Central Office (CO) and a number of ONUs near end users, i.e. remote node(s). More than one ONU may be connected to the same OLT by means of passive or in some cases, active, intermediate elements. For example, up to 32 ONUs may be connected to an OLT. PONs are called passive because optical transmission requires no power or active electronic components. In other words, other than at the central office and subscriber endpoints, there are typically no active electronics within a PON access network. Downstream signals, i.e. from the OLT to the ONU, are broadcast to all ONUs sharing a single trunk fiber. Upstream signals are signals transmitted from the ONU to the OLT.
An ONU is a device that converts incoming downstream optical signals transmitted from the OLT via a wireline fiber optical communications channel, referred to as an optical channel, into electrical signals. An ONU comprises an optical transceiver for the transmission of optical signal upstream on the optical channel. The ONU may also be called an Optical Network Terminal (ONT), which is a special case of an ONU that serves a single subscriber.
As mentioned above, the ONU is used in combination with the OLT. The OLT performs conversion between the electrical signals used by the service provider's equipment and the fiber optic signals used by the PON. The OLT coordinates the multiplexing between the ONUs at or near the various subscriber locations.
Other ways to arrange an access network include, by way of example and not limitation, the interconnection of centralized terminals such as Ethernet aggregation switches to remote devices such as digital subscriber line access multiplexers (DSLAMs) by dedicated fibre optic links, digital subscriber lines (DSL), terrestrial microwave links or otherwise.
Energy conservation in communications networks is an important issue. Potential solutions to improve energy conservation through reduced power consumption within optical access networks have been explored. These solutions may have impact on improving the equipment performance and service longevity in battery-powered operation, as well as on energy conservation and CO2 emission in general.
The term power refers to the ability to do work on a continuing bases, while the term energy is a measure of the amount of work done during an interval, that is, power*time. Therefore, energy may be saved or conserved, while power may be reduced. Throughout the industry, the term power is commonly used to refer to both. It is to be understood in the following description that terms such as power saving imply power reduction for a period of time, with the purpose of energy saving.
A current power saving mode conserves energy by implementing sleep cycles to power off one or both directions of the transceiver in the remote node(s) at certain times. Thus, at any given time, the transceiver, and hence the communications channel to the centralized unit (e.g. an OLT), may be in a so-called sleep mode or so-called awake mode, and it may use a wake-up timer to change between the modes. In order to support remote node(s) wake-up, sleep cycles are provisioned by the centralized unit, typically in the order of 10-100 milliseconds. Only when the sleep cycle expires, does a sleeping remote node(s) have the chance to wake up to receive downstream data traffic. When there is no downstream data traffic to a sleeping remote node(s), the remote node(s) still has to be awakened when the wake-up timer expires, i.e. when the sleep interval expires. Frequently turning the transceiver in the remote node(s) on and off contributes to extra power consumption. When there is downstream data traffic destined to the remote node(s), and the remote node(s) is still in sleep mode, the centralized node has to buffer the data traffic until the wake-up timer expires. The necessary buffer memory adds cost and power consumption to the centralized unit, and may degrade the end user's quality of service. In the following, the term sleep mode is used in relation to a remote node, a transceiver, a transmitter, a receiver, a communications channel, or a remote node's communication interface, while still referring to the same scenario. All of these usages refer to the case when a remote node's communication interface, i.e. the optics and possibly some part of the electronics are in sleep mode. The consequence of this is that the communication is unavailable, or sleeping, in at least one direction, depending on whether the remote node's transmitter or receiver or both, is powered down.
Another power saving mode is power shedding, in which non-essential services are switched off when the remote node(s) goes into battery operation mode after e.g. a commercial power failure. Power shedding is intended to reduce the demand for battery power and prolong the survival time of the remote node(s), while still maintaining lifeline Plain Old Telephone Service (POTS). The current definition of power shedding mode still maintains the transceiver on, while just powering down other selected elements in the remote node(s). However, one of the main power consumption contributors in the remote node(s) is the optical transceiver module. Additional energy may be saved by combining power shedding with sleep mode.
It will be appreciated that delay, buffer memory and service quality issues encourage sleep cycles to be as short as possible, while energy conservation would be better achieved if it were possible to extend sleep cycles, possibly indefinitely.
Referring to the example of the PON, the embodiments herein describe a PON ONU that also comprises a wireless interface device, and in which the wireless channel(s) is used to allow the ONU to better conserve energy by sleeping while at the same time providing better service than would be possible without the wireless channel(s). The embodiments herein take advantage of the fact that radio technology, e.g. as used in the cellular network, is far more efficient in its use of remote node battery power than is possible with current fiber optic or DSL interface technology. The sleeping ONU(s) sends and receives status reports about data traffic arrival and other significant events (such as the need for control or management transactions or alarm reports) by way of its wireless channel(s), allowing the relatively power-hungry optical interface to remain powered down.
Further, control and management data traffic or bearer data traffic may be exchanged over the wireless channel(s), in lieu of the optical channel, under various circumstances, such as light data traffic load or failure of the optical channel, but also conditioned on the relative data traffic load of the wireless channel(s). The evaluation and decision logic may be a functional component in the PON OLT.
In a plurality of telecommunications passive optical networks, each PON comprises a tree-structured fiber optical distribution network with an optical line termination at the head end and a plurality of optical network units, one at each leaf of the tree. Although described in PON terms, the embodiments herein are also suitable for direct point-to-point channels between the centralized unit and the remote unit(s).
It may be assumed that the OLT and the ONUs support energy conservation measures. In such sleep modes, the ONU powers down part or all of its transceiver from time to time, and is consequently temporarily incapable of transmitting upstream data traffic, or receiving downstream data traffic, or both, on its fiber optical interface. The ONU may awaken from sleep mode under the control of a timer, because of local circumstances such as the arrival of upstream data traffic, or, when the ONU is capable of receiving it, a wakeup command from the OLT.
In the embodiments herein, it is assumed that the ONU(s) is further equipped with a wireless radio interface that is capable of communicating with a nearby radio base station via a wireless channel(s). The radio base station is understood to serve ONUs that are members of possibly more than one PON, and may serve other data traffic as well, for example from cell phones in its vicinity (not shown in the figures).
The radio base station is equipped with a communications channel to each OLT whose ONUs it serves. The channel has sufficiently large capacity and sufficiently low delay to not constrain the functions described herein.
As described above, existing embodiments represent a tradeoff between the cost and power of buffer memory, user quality of experience, and energy conservation, in which at least one of these factors is likely to be at least somewhat unsatisfactory.